The De Vedrine family leaves the courthouse in Bordeaux after Thierry Tilly was sentenced to eight years in prison. Photograph: Jean-Pierre Muller/AFP/Getty Images

A self-styled 'guru' has been sentenced to eight years in prison for cheating three generations of an aristocratic French family out of their fortune by making them believe they were under threat from a secret masonic plot.

In what the court described as a "machiavellian plot", he tricked them into handing over up to €4.5m (£3.6m), and eventually made the family flee to Oxford, persuading them he was a former secret services agent and there was a plot against their lives. The family members, aged 16 to 89, described being in his sway for around nine years until 2009.

Tilly, 48, who met the family when he worked as an administrator at a school run by one of the De Vedrines sisters, was convicted of psychological abuse and deprivation of civil rights.

His accomplice, Jacques Gonzalez was sentenced to four years in prison.